Television receivers have evolved and improved over the years since being first available as a consumer purchasable item, however the standards of frequency allocations and signal formats have remained virtually constant. A manufacturer will either manufacture and or purchase subassemblies having been manufactured elsewhere, preparatory to the final assembly of each television set. In North America for example, a family of internal electrical standards or preferences evolved such that a subassembly manufacturer might supply an elemental circuit for any of different television sets. Such subassemblies are compatible with input and output parameters of frequency, signal amplitudes and signal formats. Thus any given set design may be assembled with any of various subassemblies having been supplied from any of various manufactures. A manufacture specializing in a particular subassembly may supply several different set assemblers and hence is often able to volume manufacture such subassembly at a lesser cost than would a set assembler. If one is to observe the circuit elements of a television receiver one will usually find parts such as, circuit boards, discrete components and integrated circuits identified with trademarks of various manufacturers.
Decades ago, before cable distribution of television program signals became common, television receivers were limited to receiving any one of at most 12 channels which occupy two bands of frequency, a lower band of 54 to 88 MHz and an upper band of 174 to 216 MHz. Each channel was received by a dedicated RF filter paired with a corresponding tank circuit, one pair of which being selected by manual rotation of a so called turret tuner. The RF filtered incoming signal was converted to an intermediate frequency typically at about 43 MHz, by a mixer driven from a local oscillator which was controlled by the corresponding tank circuit. An active band pass filter referred to as an intermediate frequency (IF) strip amplified the converted signal before video, and audio, detection and on following signal processing.
Recently advances in the manufacture of analog integrated circuits have revolutionized the manufacture of colour television receivers. Even more recently advances in the operating speeds of digital circuits, for example digital signal processors (DSPs), memories, microprocessors, analog to digital converters and codecs and the ever lower costs of these circuit elements, have spurred their use in applicable areas of television receivers. As well as cost benefits, improvements in picture display and sound reproduction have accrued. Consequently cost reductions have facilitated practical supply entry of high definition television (HDTV) receivers into the high end of the retail consumer market. Never the less realization of the dream of providing the whole of the electronics in a single integrated circuit remains ever elusive. For example analog circuit elements and digital circuit elements do not integrate easily in a single circuit substrate. Optimal circuit production yield and performance entertain dissimilar geometries, doping and processing requirements, which are virtually mutually exclusive. The requirements of signal reception dictate analog circuit functionality to derive a relatively constant signal, which may be processed by digital circuitry. Integrated digital circuitry ultimately provides digital composite video and digital composite audio signals for display and reproduction. The operating requirements of cathode ray tube operation and sound reproduction ultimately require relatively high power circuitry of an analog nature. Hence the modern television receiver yet includes a multiplicity of integrated and discrete devices often produced at several different sources and typically compatible with long established signal formats.
FIG. 1 is a block schematic diagram of a typical example of a state of the art television receiver. A pass band filter 20 passes signals appearing at its input 20a and having frequencies in a range of 55–806 MHz, to an integrated tuner circuit chip 10. A first mixer 11 mixes a variable frequency local signal having a frequency of between 1.094–1.845 GHz selected to up convert a desired channel frequency from the band pass filter 20 to generate a sum signal frequency centred on 1.9 gigahertz. A channel pass band filter 21 receives the output of the first mixer 11 and attenuates all but those signals of frequencies in the desired channel. A second mixer 12 in the integrated circuit chip 10 mixes a fixed local signal with signals from the band pass filter 21 to down convert these signals to about 43.75 MHz, the traditional standard intermediate frequency. By so doing the buffer 13 is able to amplify signals, passed by an IF pass band filter 22, and provide the amplified signals for video, and audio, detection and on following signal processes. The standard intermediate frequency output from the integrated tuner chip permits the use of virtually any typical TV industry circuitry. One or more of the filters, 20, 21, and 22 is usually a discrete element such as a surface acoustic wave (SAW) device. Although this necessitates off chip connections at considerable expense by means of beam leads or the like, the performance advantages of one or more off chip filters is usually required.
The detection and following signal processing, in FIG. 1, are exemplified as being performed by a TV processor 26 in a microcomputer chip 24. An analog to digital converter circuit 25, in a microcomputer chip 24, provides digital signals representing quantitized samples of the down converted signals from the buffer amplifier 13. The digital signals are in a preferred form for the on-following signal processing which is effected by a TV processor 26 preparatory for utilization by TV display and sound reproduction elements 27.
Although the TV industry spans many decades the introduction of digital TV processors is a relatively recent event. Examples of receivers are published in U.S. Pat. No. 6,177,964 issued to Birlson et al, wherein an analog integrated circuit tuner with several off chip filter devices is intended to provide a picture carrier at 45.75 MHz. On following analog processing circuitry may be included or separate digital processing circuitry is mentioned as an alternative.
Other examples of HDTV receivers are published in U.S. Pat. No. RE37,326, issued to Kim, wherein an analog integrated circuit tuner utilizing an IF SAW filter is intended to provide a 44 MHz output. The design of the SAW filter is simplified by further filtering by a VSB filter. The VSB filter is exemplified as being a FPLL circuit that produces quadrature I and Q outputs which are subsequently sampled at a 10.76 MHz rate and converted to digital signals. The digital signals are square root raised cosine (SCR) filtered and then subtracted one from the other to provide a digital composite video signal.
Of interest, in the U.S. Pat. No. 5,784,414, Bruekers et al are concerned with power consumption of high speed digital circuit elements in a receiver of signals in the FM and or TV broadcast bands. They teach a particular digital circuit design which reduces the required speed of operation and achieves a corresponding reduction in power consumption. Although Bruekers et al have little to offer as to a preferred form of circuit structure, the commercially viable choice is that of one or several integrated circuits. More recently, U.S. Pat. No. 5,930,488, entitled SEMICONDUCTOR INTEGRATED CIRCUIT DEVICE WITH A DATA TRANSFER CONTROLLER AND A MEMORY STORING DATA TRANSFER PARAMETERS, teaches a single chip microcomputer which includes an A/D converter. Even more recently, U.S. Pat. No. 6,286,065, titled MICROCOMPUTER HAVING A BUILT-IN A/D CONVERTER WITH A RESISTOR BETWEEN AN EXTERNAL TERMINAL AND AN I/O CIRCUIT, teaches cost reduced structures by virtue of having one less external terminal.
As digital TV processors are highly specialized apparatus and are expected to be serving a vast market place, it is expected that digital TV processors will experience accelerated development. Various TV processors will likely be based in solid state technologies not strictly limited to the currently popular complimentary metal oxide silicon (CMOS) based microcomputers and digital signal processors. Reductions in size, power consumption and cost, will be accompanied by improvements in speed and TV signal processing functionality. Presently microcomputer integrated circuit chips which accept an analog signal input include at least one A/D converter circuit. In contrast to the exclusively digital circuits of the digital TV processor 26, the A/D converter circuit 25 includes analog circuit elements as well as digital circuit elements. The analog circuit elements by virtue of their physical characteristics, determine the function speed and accuracy of the A/D conversion process. Hence anything less than the optimal circuit element geometries and the optimal analog integrated circuit manufacturing processes can result in less than optimal digitization and thus jeopardize the overall TV receiver's functionality. Developers of integrated circuit designs tend to specialize exclusively in only one of two disciplines, either analog or digital. Cooperation between these disciplines often boarders on the impractical. Furthermore fabrication processes optimized to digital circuit manufacture are in essence mutually exclusive of fabrication processes optimized to analog circuit manufacture. These contrasts between the digital and analog technologies are a serious impediment to the expeditious future development of digital TV processors.
A solution to this impediment is envisaged wherein the typical limitation of a 40 MHz or so analog interface between a tuner and on following processing circuitry is removed and a digital signal interface provided in its place. This permits the processing circuitry chip to be more conveniently provided exclusively by digital circuitry elements. Conversion of information, received by the tuner in a modulated analog carrier signal, is provided by an analog to digital A/D converter and is transferred to the microcomputer either on a periodic basis or on an interrupt basis, for example. The A/D converter is advantageously manufacturable in integrated circuit form within the integrated TV tuner circuit chip. As the digital circuit elements of the A/D converter 25 are relatively of little bulk, characteristics of optimized smallness and miserly power consumption are relatively insignificant. Hence digital circuit geometries can be utilized to provide for satisfactory digital circuit functionality in spite of being produced by preferred analog circuitry manufacturing processes.